1. Field of the Invention
This invention relates to a photographic processing method and tank for processing silver halide photosensitive material (often abbreviated herein as "photosensitive material").
2. Prior Art
Black-and-white photosensitive materials after exposure are processed through a series of steps including black-and-white development, fixation and washing and color photosensitive materials after exposure are processed through a series of steps including color development, desilvering, washing and stabilization. There are used black-and-white developer for black-and-white development, fixer for fixation, color developer for color development, bleaching, blix and fixing solutions for desilvering, city water or deionized water for washing, and stabilizer for stabilization. Photosensitive materials are generally processed by dipping them in the respective solutions which are normally adjusted to a temperature of 20 to 50.degree. C.
Among these steps, the developing step is a step wherein a developing agent which is a reducing agent acts on exposed silver halide grains in the photographic emulsion for reducing Ag.sup.+ into Ag. Silver images are created in this way in black-and-white photography. In the case of color photography, an oxidant of color developing agent reacts with a coupler to form a dye image corresponding to a silver image. The developers experience a lowering of developing power due to deterioration by air oxidation during quiescent periods or the like. It is believed that the developing power is lost mainly because the developing agents and preservatives therefor are oxidized.
For avoiding such developer deterioration, a typical prior art approach is to replenish an increased amount of developer. Increased replenishment, however, results in increased usage of chemical agents and water, which is undesirable particularly from the standpoint of environmental protection requiring resource saving and waste liquid reduction. Further, since color developing agents are expensive, their increased consumption is against economy.
Subsequent to the color development step in the color photography is carried out a desilvering step, which involves several modes of performing bleaching and fixing steps in a common bath or separate baths, or performing bleaching and bleach-fixing steps in separate baths. The mode of performing bleaching and fixing steps in separate baths has the advantage of stable processing. The mode of performing bleaching and bleach-fixing steps in separate baths draws attention because of promoted desilvering (see Japanese Patent Application Kokai=JP-A 75352/1986).
Used in the bleaching step are bleaching solutions which contain bleaching agents or oxidizing agents. Exemplary bleaching agents are ferric complexes of aminopolycarboxylic acids and aminopolyphosphonic acids or their salts. Among others, ferric ethylenediaminetetraacetate complex is most often used while ferric 1,3-diaminopropane-tetraacetate complex and analogs are also known as having high oxidizing power.
In the bleaching step, the silver resulting from the color development step undergoes oxidation reaction under the action of the bleaching agent which is an oxidizing agent while the bleaching agent itself is reduced. Therefore, the bleaching solution lowers its bleaching or oxidizing power as photosensitive materials are processed. A significant loss of oxidizing power occurs particularly when processing a great amount of photosensitive material or over-exposed photosensitive material.
The oxidizing power of bleaching agents can be restored, for example, by aerating the bleaching solution to increase the redox potential thereof. The aeration method, however, can introduce bubbles in the solution, bringing the problems that the bubbling solution can spill out of the bleaching tank contaminating the surroundings and that bubbles can splash over an adjacent tank contaminating the solution therein. The latter problem becomes more serious if the solution in the adjacent tank is a color developer as is often the case, because such entrainment causes the color developer to deteriorate and lower its developing power.
In the fixer is contained a fixing agent for dissolving the silver which has been oxidized by the bleaching agent. The fixing agent and preservatives therefor in the fixer are prone to oxidation with time during quiescent periods when no photosensitive material is processed. Once oxidized, these agents can decompose into sulfides which would cause sulfidation problems including photosensitive material surface contamination. Deficient fixation or desilvering is also a problem. These problems associated with oxidation are aggravated by entrainment of bleaching solution by the traveling photosensitive material.
The above-mentioned sulfide formation and deficient fixation problems occur likewise in fixers for black-and-white photography.
Heretofore, these problems were overcome in both black-and-white and color photography by increasing the amount of fixer replenished. However, increased replenishment is undesirable in view of resource saving and used solution disposal as previously described. Processing solutions containing bleaching or fixing agents commonly suffered from the above-mentioned problems associated with desilvering step.